1. Field of the Invention
The present invention relates generally to space diversity receivers, and more particularly, to an improved space diversity receiver which has at least two antennas spaced from each other and is operative to select the best one of signals received respectively by the antennas to obtain reproduced video and/or audio signals therefrom.
2. Description of the Prior Art
In a television broadcast signal receiving system provided in an automobile, it is prevalent to use a space diversity receiver since the location of the receiver changes over a relatively broad area and the intensity of the electric field of a television broadcast signal varies quite frequently. The space diversity receiver used in the automobile is accompanied with, for example, four antenna connectors mounted on middle and rear parts of each of left and right sides of a cabin portion each to be coupled with an antenna.
In such a space diversity receiver, during a specific period corresponding to, for example, a beginning portion of a vertical blanking period of the television broadcast signal to be received, output signals of a signal processing circuit block produced respectively based on signals obtained from the antenna connectors are compared in quality with one another to select one of the antenna connectors through which a signal giving rise to the best output signal of the signal processing circuit block is introduced, and then during a period successive to the specific period, the signal introduced through a selected antenna connector is supplied to the signal processing circuit block. The signal processing circuit block produces a received signal output based on the signal introduced through the selected antenna connector, from which reproduced video and audio signals are produced.
In the space diversity receiver as described above, the signal obtained from the antenna connector constitutes an antenna output signal when an antenna is connected with the antenna connector. However, frequently all four antenna connectors are not each provided with an antenna, for example, only three of them are provided with antennas. In such a case, the signal obtained from the antenna connector which is not connected to an antenna does not constitute the antenna output signal.
In such a case, in determining the signal giving rise to the best output signal of the signal processing signals obtained respectively from the four antenna connectors, the signals are selectively sampled for every predetermined short period and successively supplied to the signal processing circuit block without checking whether the four antenna connectors are all provided with respective antennas or not. In the signal processing circuit block, output signals are produced based on the sampled signals, respectively, and compared with one another so as to determine the best output signal.
Under such a condition, the output signals of the signal processing circuit block and derived to be interconnected with a discontinuous portion between each successive two so as to produce a received signal output. Since the signal sampling operation is performed in, for example, the vertical blanking period of the television broadcast signal to be received, no substantial trouble or problem is brought about on a picture produced in accordance with the reproduced video signal which is obtained based on the received signal output derived from the signal processing circuit block even if the received signal output derived from the processing circuit block contains the discontinuous portions therein. However, in respect of a sound produced in accordance with the reproduced audio signal which is obtained based on the received signal output derived from the signal processing circuit block, there is a disadvantage that harsh noise occurs in response to each discontinuous portion contained in the received signal output derived from the signal processing circuit block.
Accordingly, it is desired that the signal sampling operation for selecting the antenna connector through which the signal giving rise to the best output signal of the signal processing circuit block is performed a minimum number of times in order to suppress the harsh noise contained in the sound produced in accordance with the reproduced audio signal.
Further, in the case where the signals obtained respectively from four antenna connectors, at least one of which is not provided with the antenna, are subjected to the signal sampling operation, the signal processing circuit block cannot produce a correct output signal thereof during a short period in which the signal obtained from the antenna connector with which the antenna is not provided is supplied thereto and therefore the received signal output is intermittently derived form the signal processing circuit block to include lacking portions. A sound produced in accordance with the reproduced audio signal obtained based on such a received signal output as to include the lacking portions contains also harsh noise resulting from the lacking portions of the received signal output.